Lifting cranes
What lifting machines does the slinger service?
Lifting machines (Fig. 2.1) that are serviced by slingers include load-lifting cranes, pipe-laying cranes, and manipulator cranes.
Pipe laying crane is a self-propelled lifting machine with a side boom 2 for lifting, transporting and installing pipes. The base machine for a pipe-laying crane is usually a crawler tractor 1.
Crane arm- This is a lifting machine consisting of a crane installation 3 mounted on a vehicle 4 or foundation.
What types of cranes are there?
Overhead cranes- these are cranes in which the load-handling member 5 (see Fig. 2.1) is suspended from a cargo trolley 7 moving along a bridge 6. These include overhead and gantry cranes.
Cable type taps- These are cranes in which the load-handling member is suspended from a load trolley moving along supporting ropes 8. This type includes cable and cable-bridge cranes. The cable crane has load-bearing ropes fixed in the upper part of the support masts 9.
Jib cranes- these are cranes with a load-handling member
suspended from a boom or load trolley moving along the line le. The jib type includes portal, tower, railway and jib cranes.
A portal crane is a rotating crane located on a portal 10, intended for the passage of railway or road transport.
A tower crane is a rotary crane with a 2-boom attached to the top of a vertical tower 11.
A railway crane is a crane mounted on a platform 12, moving along the railway track.
A jib crane is a rotating crane in which the boom is fixed to a rotating platform placed directly on the running device. Jib cranes differ in the type of running gear:
Ø automobile crane installed on a vehicle chassis;
Ø pneumatic wheel crane mounted on a pneumatic wheel chassis;
Ø short-base crane installed on a short-base chassis;
Ø crane on a special chassis, mounted on a special automobile-type chassis;
Ø crawler crane mounted on a crawler undercarriage.
What are the main parameters that characterize the crane?
Load capacityQ(Fig. 2.2) - the maximum mass of cargo that the crane is designed to lift and move under given operating conditions. The load capacity includes the mass of removable lifting devices and containers used to move the load.
DepartureL- the horizontal distance from the axis of rotation of a jib-type crane to the axis of the load-handling member.
Load momentM - the product of the load capacity and the corresponding reach M= QL(t-m).
spanS- horizontal distance between the axes of the crane track rails for overhead cranes. Reach and span are parameters characterizing the size of the area served by the crane.
The crane is an indispensable assistant in many industries. The need for it arises when you need to move loads vertically or the load is so heavy that it is not possible to remove or load it into a car or railway transport manually.
There are purely narrowly targeted cranes. Such as railway. Their main purpose is to load and unload trains. Sometimes they are used to organize warehouses near railway tracks. In rare cases, to remove rubble and build the same railway tracks.
Stationary cranes. They are used by large enterprises where it is necessary to constantly move cargo from place to place. These include any ports and large warehouses with constantly changing saturation. Those. The crane's life will be exhausted before it becomes necessary to move it. - a bright representative of this type of load-lifting cranes.
Truck-mounted cranes. Extremely high mobility, extremely low load capacity - most construction and residential complex enterprises love them for these qualities. In these organizations, idle work directly affects the cost of work and the loads are usually not so heavy.
Cranes on their own. These cranes are able to move not due to the engine of the car or train on which they are installed, but, as they say, on their own two feet. These cranes are used in cases where there is no need to install a stationary high-capacity crane covering the entire work site, and it is not financially feasible to install several cranes. These cranes are mainly used on construction sites, where it is almost impossible for such a crane to travel.
The supporting structure determines the basic operating height of the crane. For truck cranes, this is the height of the vehicle itself. For a tower it is called “Supporting Structure”. For an overhead crane, this value exceeds the lifting height of the load.
For a tower crane this is a boom. For some cranes, the boom changes size, for some, the location of the load on the boom changes. In an overhead crane this is called a girder. The boom/beam with the load attachment point can be connected by ropes, chains, etc. All this together allows you to position the load in space.
In everyday communication, a load-handling member is an attachment to a crane. Something with which the load is grabbed and held. Modern cranes are usually equipped with all possible grips for any job. You just need to select the one you need. For example:
An overhead crane is a mechanism that is used to move loads. For the 80s XX century The production of devices peaked, Soviet factories produced from 6,000 to 7,000 units of equipment every year. In the 90s production volume has fallen, and today no more than 1,500 cranes are produced in all countries of the former USSR.
The general structure of the overhead crane is reliable; manufacturers make the main components and other structural elements from high-quality steel. The lifting machine consists of the following:
Devices for grasping cargo are installed on a trolley; the equipment is used in all spheres of the national economy. Most often it is used to move heavy or bulky loads. In all other cases, enterprises can make do with cranes of lower lifting capacity.
Bridge mechanisms can be found at construction and industrial sites, ports, and workshops of enterprises. The equipment is used in any climatic zones. It is often installed indoors, but it is also suitable for outdoor work.
The advantage of the systems is that they can operate at the entire height of buildings, but the disadvantage is that the lifting devices are stationary.
If we talk about the general structure, the bridge is a one- or two-beam structure along which a cargo trolley moves. The electrical equipment is located on the bridge part, and the mechanisms that are used to move goods are located on the trolley.
In order to hold the load suspended and regulate the speed of its lowering, a brake is used. This mechanism is necessary to quickly stop moving parts of a structure, such as a trolley or a bridge.
Manufacturers equip models with the following braking systems:
The shoe brake consists of 2 shoes, which are located on both sides of the pulley. This position allows you to evenly distribute the load on the shaft. The brake pulley is installed before the gearbox, this makes braking easier.
The role of the brake pulley is performed by the clutch; it connects the electric motor to the gearbox. The brake is mounted so that its pads clamp the part of the coupling connected to the gearbox.
The brake mechanism must be closed with a load. To do this, it is installed on the lever in such a way that it does not move to the side and does not fall. A spring can be used for closure. In this case, it is placed in a sleeve, and it can also be equipped with a centering rod.
The brake must be protected from moisture. In order for the mechanism to work better, a brake band is riveted onto the brake pads. This increases friction between the pulley and the pad.
The cart can move at different speeds. If it does not exceed 32 m/min, the device for moving goods need not be equipped with a braking system. Under these conditions, braking occurs independently, the braking distance is not exceeded.
All braking systems can be divided into stop and release. The former are used to stop the device, and the latter are necessary to slow down the descent of the load.
The brake system can be of the following types:
Manufacturers may equip the lifting mechanism with closed brakes, in which case the brake will only be released when the engine starts. In other positions the mechanisms will be inhibited.
Closed brakes are used most often because they last longer than open brakes. If they fail, then their breakdown is easier to notice. Open braking systems can complement closed ones. Using them, the crane operator will increase the accuracy of moving loads.
Bridge mechanisms can be used to move dangerous goods. These include toxic and explosive substances, as well as molten metal and acids. In this case, the mechanisms are equipped with 2 brakes. They act autonomously, replacing each other.
Manufacturers equip cranes with lifting mechanisms and place them on a crane trolley. The system consists of the following elements:
If the enterprise plans to move cargo weighing more than 80 tons, the crane must be equipped with an additional gearbox. If the need arises, it can be replaced with a reduction gear. In order to increase traction force, a chain hoist can be used. This device consists of several blocks that are wrapped around a rope or cable. Crane operators often use a double multiple hoist.
The crane cannot operate without a gearbox; they are divided into the following types:
Manufacturers equip cranes with gearboxes in planetary and rotary versions. The unfolded type is the most commonly used and is equipped with cylindrical wheels. The design of the mechanism, when compared with the planetary one, is simpler. Such systems are cheaper to repair.
The crane moves along railway rails laid on the ground. They can be narrow gauge (P18, 24, 38) and designed to form a wide gauge. In the latter case, products P4, 50, 65 are used.
Square guides can be used to move the lifting mechanism. They are made of steel, the products are distinguished by rounded edges. They are designed for operation of cranes with a lifting capacity of 20 tons and above.
To move the overhead crane, I-beams are used as tracks. To connect their ends, double-sided plates and bolts are used, but the elements are often connected by welding. When installing beams, you should pay attention to the quality of installation. There should be no displacement of elements. Only if installed correctly will the crane operate without failure, and worn rails can be easily replaced.
The crane is powered in 2 ways:
Systems of the first type are required for the operation of heavy-duty mechanisms. The tire is placed at a height of more than 3.5 m from the floor level; it must be at least 2.5 m from the bridge deck.
In the second case, a flexible electrical cable is connected to the tap and suspended on a carriage. The cable system is simpler and easier to operate. Its installation will cost the enterprise less, but it must be taken into account that it is less reliable. The trolley line is used to move the bridge beam, and the cable system is better suited for the operation of the crane trolley.
Strict requirements are imposed on electricians, because the number of operations that a crane operator performs in 1 day amounts to hundreds. They are associated with the acceleration of a cargo trolley, its braking, turning on and off additional devices, unloading, loading or moving containers and cargo from one place to another.
During operation, there is a need for emergency braking, so the crane elements are subject to high loads. All systems must be in working order; the safety of the crane operator and other people depends on this.
To organize the movement of the trolley, the bridge and the movement of goods, the following equipment is used:
The crane requires auxiliary equipment to operate. This includes spotlights and heating devices. The group includes measuring equipment and sound alarms. Tools are widely used and are needed to perform repair work.
A cargo trolley is needed to lift loads, move them along the bridge, and then install them in a new place. The crane units are located on a steel frame, which is rigidly connected to the wheels. The operation of the device is carried out by drives. The trolley moves due to the main and auxiliary electric motors. It is additionally equipped with a current collector, and there are blockers that regulate the lifting height.
In production, a situation may arise when an emergency stop of the trolley is required. Emergency braking is performed using buffers.
Cantilever bogies are used on single-beam bridge mechanisms. Double-beam ones are equipped with devices that move along the lower and upper chords of the beams.
Bridge mechanisms differ from other systems in that during operation they rely on the crane track. It is made from railway rails or square-section elements, they are made from high-quality steel.
The load-bearing beam moves along rails; they are laid on overpasses inside workshops or open areas of industrial enterprises. The cargo trolley moves along the bridge and is equipped with a winch for lifting cargo.
Companies often need to expand the functionality of lifting mechanisms, in which case cranes are supplemented with various devices. This could be a set of magnets of different power or grabs. The acquisition of additional mechanisms makes it possible to use overhead cranes not only in industrial production, but also to perform work in warehouses and in the construction industry.
The industry produces different overhead cranes, but all of them can be divided according to the following key characteristics:
If we consider the classification by area of application, we can distinguish the following types of overhead cranes:
Depending on the design, lifting systems are divided into the following:
According to the method of movement, there is the following classification:
If we consider the mechanism that is used to grab cargo, we can highlight modern grab and special systems. This group also includes casting and magnetic devices. In industry there is often a need for hooks.
Based on this feature, all lifting mechanisms can be divided into the following:
Enterprises must select mechanisms based on their cargo movement needs.
The following types of models are distinguished:
Cranes have different prices.
Manufacturers produce mechanisms that, according to their purpose, are divided into the following:
When choosing a mechanism, an organization must take into account the purpose of the goods. If they are classified as hazardous, their movement will be different.
Based on this feature, all bridge type cranes can be divided into the following:
Businesses can choose from domestic and foreign models.
Transportation of overhead cranes is carried out in different ways, but most often delivery is carried out using railway platforms. The main beams are shipped assembled. Parts of bridge structures that have large spans are transported in 2 or 3 sections.
If the lifting mechanism has a small load capacity, the carts are transported assembled. Production requires heavy-duty trolleys; they are transported in units. The frame and lifting mechanism are transported separately; if necessary, the balancers are moved from place to place.
The choice of transportation method depends on the size of the crane. If it is large, the structures are transported on separate railway platforms. It is possible to organize a coupler of 2 elements, but they are suitable for delivering cargo whose length does not exceed 17 m. For this purpose, platforms are used whose lifting capacity is 50 tons and 60 tons.
If the loads are oversized, you need to pay attention to the quality of their securing. It is important to take into account loading conditions. The parts of the crane must be securely fixed in place; to do this, wooden beams are placed under them. This reduces the mobility of the elements; they do not move during transportation. The crane is fixed to the platform using guy wires. It is necessary to make a strength calculation, determine the effective dynamic loads and the magnitude of the impact of inertial forces.
If railroad tracks cannot be used for transportation, the crane is loaded onto semi-trailers. To transport them, powerful tractors or tractors are used. The enterprise must choose appropriate courses of action.
Installing a crane requires preliminary work, which begins with the installation of crane tracks. They are laid on an overpass or on the ground. There are 3 installation options:
Installation work should be carried out by specialists; they also dismantle the overhead crane and do grounding. It requires strict adherence to safety standards. They resort to it when it is necessary to replace the old lifting mechanism. It is also necessary after completion of work on the site.
There are several dismantling options, each of them depends on what is supposed to be done with the crane next. If it is to be disposed of, the crane beams are removed from it. The structure is freed from the cable, the electric bridge motor is removed, and the cables are wound up. Spanning beams and other components made of metal are sent for scrap.
If the crane is moved to another location, the traveling mechanisms of the overhead crane and devices for moving loads are disconnected from it. In this form, the structure is transported to the work site, where it is reassembled.
The operating instructions contain information on the scope of use of lifting devices. When choosing a model, you should pay attention to the crane operating instructions; the scope of application may be as follows:
With the help of bridge systems, other loads can also be moved; for this purpose, the crane is supplemented with equipment with magnetic properties.
Repair of overhead cranes is not often required, because the structure has a long service life. Much more often it is necessary to fix minor problems and adjust the operation of the device. Before starting a shift, the driver is required to check the condition of the crane.
Diagnostics of an overhead crane, as well as routine repairs, must be performed by specialists. They are engaged in the following list of works:
Minor problems can be fixed at the enterprise, but major breakdowns require dismantling the structure. If necessary, specialists can upgrade the devices. The work is carried out in accordance with the requirements of GOST.
Specialists can replace hook suspension or cable suspension, check instruments and safety devices, and inspect suspended equipment.
Repair work is of the following types:
Planned ones are performed to prevent breakdowns. During the work, the technician diagnoses faults, lubricates mechanisms, and adjusts components. A technical inspection of the overhead crane is being carried out.
Overhaul includes a wide range of works. It is necessary for cranes whose service life has already expired. Emergency repair is needed when a device fails. The technician identifies the problem and fixes it as quickly as possible.
The electrical circuit of an overhead crane depends on the model of the device, but the following main points can be highlighted:
An electrical diagram is required in order to repair electrical equipment. It consists of special characters that characterize nodes. Rectangles represent moving contacts, filled circles indicate stationary elements. Sweeps mean drum controllers. Their position is determined by lines running parallel. They are signed with numbers at the top.
The industry produces general-purpose electric overhead cranes and other devices. Their cost is influenced by the configuration and lifting capacity of the overhead crane. Used devices are cheaper, but you can save money by purchasing a new domestic model rather than a foreign-made faucet. A 10 ton crane can be bought for 200 thousand rubles, there are models whose cost reaches 2 million rubles.
When choosing a mechanism, you need to take into account that many brands require a crane track. Small businesses can purchase a suspended bridge crane or mechanism with a lifting capacity of 5 tons.
Mikhail, 47 years old, Kaluga.
It took a long time for the company to select overhead cranes on fixed supports. We found 1 device, the price is affordable. Now there are no problems with loading.
Igor, 36 years old, Yakutsk.
Posted 11/26/2012
Types of taps
Among the designs of load-lifting cranes, there are jib-type cranes, bridge-type cranes, cranes with load-bearing ropes and stacker cranes.
1. Jib-type cranes are lifting cranes with a load-handling member suspended from a boom or a load trolley moving along the boom.
These include:
a) jib cranes - jib-type cranes with a boom mounted on the frame of the running device or on a turntable placed directly on the running frame;
b) tower cranes - jib-type cranes with a boom attached to the top of a vertically located tower;
c) portal cranes - jib-type cranes, rotary, on the portal;
d) semi-portal cranes - jib-type cranes, rotary, on a semi-portal;
e) mast cranes - jib-type cranes, rotating, with a boom hinged to a vertical mast having lower and upper supports. In this case, for cable-stayed cranes the upper support is secured by means of guy ropes, while for rigid-legged cranes it is rigidly secured;
f) cantilever cranes - jib-type cranes, the load-handling member of which is suspended on a console connected to a column or supporting part of the crane or on a trolley moving along the console. The group of jib cranes includes column mounted, wall mounted jib crane, mobile jib crane and bicycle crane.
2. Bridge-type cranes are load-lifting cranes with a load-handling member suspended from a load trolley, a rotating boom on a load trolley or a hoist moving along a movable bridge.
These include:
a) overhead cranes - bridge-type cranes with a bridge directly supported on an overhead crane runway;
b) gantry cranes - bridge-type cranes with the bridge resting on the crane runway using two support posts;
c) semi-gantry cranes - bridge-type cranes with the bridge resting directly on the crane track on one side, and with the help of a support stand on the other.
3. Cranes with load-bearing ropes are load-lifting cranes with a load-handling member suspended from a load trolley moving along load-bearing ropes fixed to supports. For cable cranes, the supporting ropes are fixed in the upper part of the supports, and for bridge-cable cranes - at the ends of the bridge mounted on support posts.
4. Stacker cranes are load-lifting cranes equipped with a vertical column with a device for stacking loads moving along it. In an overhead stacker crane, the column is suspended from a load trolley moving along a mobile bridge, while in a rack stacker crane, the vertical column moves in the aisle between the racks.
In addition to the classification of cranes by design, there are classifications based on other criteria:
by design of the load-handling device and by purpose - hook, grab, magnetic, magnetic-grab, traverse, claw cranes, muldo-magnetic, muldo-grab, muldo-loading, pin, piledriver, hardening, foundry, landing, cranes for stripping ingots, well, forging, container and etc.;
if possible, movement - stationary, attached, self-elevating, adjustable, radial, mobile, self-propelled, trailed;
according to the design of the running gear - rail, railway, walking, automobile, cranes on an automobile chassis, crawler, tractor, pneumatic code, floating;
by type of mechanism drive - manual, mechanical, electric, hydraulic, pneumatic, cranes with a combined drive.
All about lifting cranes. General information.
A crane is a cyclic lifting machine with a reciprocating movement of the load-handling member; used for lifting and moving loads. The work cycle of a load handling device consists of picking up a load, a working stroke for moving the load and unloading, and an idle stroke for returning the empty load-handling device to the place where the load is received. The movements of the lifting gear can be both working and installation for periodically changing the position of the crane, boom, etc. The main characteristic of the lifting gear is the lifting capacity, which is understood as the largest mass of the load being lifted, and in the case of replaceable lifting devices, their mass included in the total carrying capacity.
Depending on the design and the adopted operating scheme, pumps can be rotary or non-rotary. Slewing cranes can be mounted on rails - railway and rolling rail cranes; on trackless tracks - pneumatic wheels, automobile and caterpillar vehicles; on the walls and roofs of buildings - wall-rotating and roofing; on pontoons and vessels - floating and ship-borne. There are also rotary gearboxes that move along two rails located at different levels (bottom and top) - the so-called. bicycle cranes. Railroad, pneumatic-wheeled, automobile, and tracked rotary cranes are often combined under the common name of jib self-propelled cranes. The rotating part of the machine rests on a column (crane on a fixed or rotating column) or on a turntable with wheels, rollers, or balls (crane on a turntable). The rotating part can have the shape of a high tower - tower cranes, masts - mast-jib cranes (rigid and cable-stayed). It can be installed on a portal - portal cranes. Rotary cranes can have a constant or variable reach (the distance of the load from the axis of rotation of the crane), which is changed by swinging the jib (boom) or moving the cargo trolley along it.
Fixed cranes include overhead cranes of the span type (overhead cranes and material handlers), as well as wall-mounted jib cranes. Overhead cranes have a rolling bridge that moves on rails laid on the walls of buildings or on special overpasses outside the building. A cargo trolley with a lifting winch moves along the bridge; in some designs, the cargo trolley is equipped with a rotating boom. Wall-mounted jib cranes consist of a cantilever wall truss and a load trolley moving along it with a lifting winch. Reloaders are similar in design to overhead cranes, but their bridge has high supports (legs) that move along ground tracks. For large spans they are called bridge loaders or levellers, and for small spans they are called gantry cranes. However, there is no clear division. Reloader bridges may have fixed or retractable consoles; A cargo trolley or a rotary crane moves along the bridge. Cantilever cranes designed for loading (unloading) ships, the so-called. coastal cantilever cranes can also be installed on ships (ship cranes). A special type of material handler is a cable crane, in which the cargo trolley is moved using a traction rope along a support rope stretched between 2 rolling towers or stationary masts. A type of cable cranes are bridge-cable cranes, in which the supporting rope is attached to the ends of the bridge truss. Monorails are structurally similar to crane devices, the trolleys of which have lifting mechanisms.
In modern construction conditions, helicopter cranes with devices for grabbing cargo are also used. With their help, work is carried out in hard-to-reach areas
Areas of application for cranes Overhead cranes are typical production equipment. workshops, power plants, indoor and outdoor warehouses. Their lifting capacity reaches 500-600 tons, spans (distances between the axes of crane rails) - 50-60 m, possible lifting height of cargo - 40-50 m and in a special version up to 500 m; bridge speed (working movement) -30-160 m/min, cargo trolley - 10-60 m/min, load lifting up to 60 m/min.
The bridge can accommodate 2 freight trolleys on one or two (adjacent or double-row in height) tracks. General-purpose overhead cranes include hook, magnetic, grab, and magnetic-grab cranes. Single-beam hook cranes of the simplest type (see Beam crane), supporting and suspended, have a self-propelled electric hoist as a load trolley. A special group includes metallurgical bridges (foundry, filling, well, for “stripping” ingots, etc.), which are equipped with special load-handling devices and control mechanisms. One of the varieties of pavement pallets is a stacker crane with a cargo trolley that has a rotating column along which a fork moves, carrying a package of cargo on a pallet and allowing stacking and dismantling of package stacks.
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LOAD-LIFTING CRANE, a cyclic machine designed for lifting and horizontal movement of cargo held by a load-handling device until unloading. A lifting crane operates within a limited work area (construction site, workshop, terminal, warehouse, etc.). The main characteristic of a load-lifting crane is its lifting capacity, which refers to the largest mass of the load being lifted.
Historical reference. The simplest lifting machines, used for excavation work in construction, in mines and mines, until the end of the 18th century were made of wooden parts and had a manual drive. By the beginning of the 19th century, wear parts began to be replaced with metal ones. In the 1820s, the first lifting machines made entirely of metal appeared, first with a manual drive, and in the 1830s with a mechanical drive. The first steam crane was created in Great Britain in 1830, a crane with a hydraulic drive was created there in 1847. The electric motor was used on load-lifting cranes in 1880-85 almost simultaneously in the USA and Germany; in 1895 the internal combustion engine was used. The load-lifting cranes had a bridge truss and a single-engine drive.
Modern type lifting cranes began to be produced in Russia at the end of the 19th century at a number of factories (Putilovsky, Bryansk, Kramatorsk, Nikolaevsky, etc.). In the 1920s, a new branch of transport engineering was created with specialized factories producing cranes for various purposes. The main direction of production development is the introduction of automated control, increasing lifting capacity, specialization and ensuring the reliability and safety of crane equipment.
Classification. Load-lifting cranes differ in design, type of load-handling device corresponding to the nature of the work performed, the specified trajectory of the load; angle of rotation of the working parts, running gear, type of mechanism drive. The variety of designs of load-lifting cranes ensures their wide application. Based on the characteristic features of their design, load-lifting cranes are divided into overhead cranes, jib cranes, and special ones often created on their basis.
Bridge cranes have a truss structure along which a cargo trolley moves with a load-handling device suspended on it by means of ropes (hook suspension, lifting electromagnet, grab, etc.). The trolley moves across a truss structure supported by bridge beams, which can move along a special crane track laid on an overpass or load-bearing beams of a workshop, warehouse, etc. (Figure 1). Load-lifting cranes of this type include a gantry crane, the cargo trolley of which is mounted on rigid racks (Figure 2). The entire structure moves along a rail track or concrete base. The lifting mechanism of the crane is a hoist or winch mounted on a cargo trolley. The trolley movement mechanisms can have a flexible traction drive (chain or rope) or drive wheels mounted on the trolley frame or on running beams that have special balancing trolleys and drives with shoe or disc brakes. The lifting capacity of typical overhead cranes is 500-600 tons; goats - up to 1600 tons.
Jib cranes have the most varied designs: equipped with replaceable booms of various lengths, telescopic or truss (straight or curved), providing the required scope of work; equipped with specialized lifting equipment (cargo trolley or hoist); depending on the location of the work, they have appropriate supporting and running devices. Based on the design features and location of the boom, lifting cranes are distinguished that are designed to perform specific work. There are gantry cranes (Figure 3) with a boom mounted on a slewing gantry or self-propelled cranes with a vehicle- or crawler-mounted undercarriage; tower - with the boom located at the top of the structure (sometimes on the portal) of the tower; cable-stayed - with a boom on a foundation support with its upper end fastened with guy ropes, mast - with a rigid fastening of the boom; cantilever - when the boom is permanently attached to a wall, column (Figure 4) or on a movable cart; bicycles - with a trolley moving along a floor single-rail track and held by its upper guide. To change the length (extension) of the boom when it is hinged to a support, load-lifting cranes are equipped with a winch. Tower structures are made in the form of lattice or tubular sections connected by flanges, with the possibility of expanding them from below or from above to change the height of the load lifting. The stability of a lifting crane is usually ensured by the use of counterweights. Rotation (turning) is carried out on roller or ball slewing bearings using a gear drive or a rope drive. In the construction of high-rise buildings (100-300 m), they use attachment cranes that are attached to the wall of the tower building and built on top, and for heights over 300 m, mobile tower cranes are used, resting on the building structure from above and self-lifting using a winch that has a large pulley mechanism multiplicity. The lifting capacity of mobile cranes is from 40-300 tons, special installation cranes - up to 1600 tons.
Figure 3. Portal crane with articulated boom and grab grip.
Special cranes are designed to perform lifting and transport or technological operations, often carried out under special conditions. Such lifting cranes have the necessary mechanisms that perform specified technological operations, perform specific movements and are equipped with special load-handling devices. For most of them, the base is a bridge-type structure, which is complemented by special equipment - grab, magnetic grab, special load-handling equipment, for example, buckets for molten metal, stackers. To work in large areas (terminals, container yards), bridge loaders are used, equipped with spreaders (Figure 5) to capture and securely hold the cargo; bridge cranes, which are similar in design to gantry cranes, but have a larger bridge span, one of the supports is often connected to the bridge with a hinge, which increases the service area. In ports, warehouses for bulk materials and timber cargo, gantry cranes are used, which have a boom mounted on a full-revolving platform mounted on a portal moving along crane rails. Work on cleaning the bottom of reservoirs is carried out from floating jib-type cranes, which are also most often equipped with turntables and form a single structure with the hull of the vessel (pontoon). They are used in ports, docks and in the construction of hydraulic structures, for lifting heavy loads (up to 2500 tons). Self-propelled cranes have tower and boom structures similar to tower cranes and are equipped with outriggers (outriggers) for stability. Such load-lifting cranes are used for reloading heavy piece and bulk cargo, and are used in the installation of high-rise structures, bridge construction, debris removal, emergency response, etc.
Design features. Load-lifting cranes are divided into: stationary; attached, attached to a structure under construction; adjustable (moving them from one place to another manually or using other machines); mobile, moved from one working position to another under its own power (on a car, pneumatic wheels, caterpillar tracks and railway platforms) or using a tractor (trailer). The running device can rest on top of the crane rails (supporting) or be suspended on the lower I-beam shelves of a special crane runway (suspended). The drive of all mechanisms, as a rule, is individual from electric motors of three-phase alternating current 380 V or (if smooth speed control is necessary) direct current obtained from a generator set or from a diesel engine. To ensure safe operation, all load-lifting cranes are equipped with automatic limiters for load capacity, load lifting height, load moment on the boom, and limit switches for the extreme positions of working bodies. To stop the operation of the crane in strong winds, wind pressure indicators with alarms, shutdown drives, and anti-theft grips - rail clamping pliers - are used. At the end of the rail tracks, stops are installed for buffer devices (shock absorbers, hydraulic stops). To operate on rough terrain, load-lifting cranes are equipped with tilt indicators, and near power lines - with light and sound signaling devices about dangerous approach of the crane to the lines.
The operation of the load-lifting crane is controlled by a push-button remote control “from the floor” or by power controllers or command controllers located in the cabin. In most lifting cranes, control is provided by the crane operator, and in automated mode - using a computer. When working in hazardous conditions or with insufficient visibility from the cab, remote control is used.
Depending on the purpose and design, load-lifting cranes can have different load lifting heights, for example, for bridge cranes 50-60 m; operating speed of the bridge is 30-160 m/min; cargo trolley up to 60 m/min; For boom cranes, the boom lifting speed is 1-3 minutes; boom reach 60-100 m.
Lit.: Load-lifting cranes: In 2 books. / Edited by M. P. Alexandrov. M., 1981; Petukhov P. Z., Ksyunin G. P., Serlin L. G. Special cranes. M., 1985; Zertsalov A. I., Pevzner B. I., Benenson I. I. Stacker cranes. 3rd ed. M., 1986; Vainson A. A. Lifting and transport machines. 4th ed. M., 1989; Aleksandrov M.P. Load-lifting machines. M., 2000.
